RABIES
Rabies virus is an RNA virus and is a member of the family Rhabdoviridae. Rhabdos, meaning "rodlike," refers to the distinctive elongated shape of these virusesThe virus infects the central nervous tissue and salivary glands of a wide range of mammals, and is usually conveyed by saliva through bites or licks on abrasions or on intact mucous membranes. Humans are most frequently infected from dogs. In Europe, the maintenance host is the fox, bats have accounted for most cases of human rabies in the United States
Pathogenesis
Having entered the human body, the virus replicates in the muscle cells near the entry wound. It penetrates the nerve endings and travels in the axoplasm to the spinal cord and brain.In the CNS the virus again proliferates before spreading to the salivary glands, lungs, kidneys and other organs via the autonomic nerves.
Clinical features
Incubation period (1–3 months) Prodrome (1–10 days) Acute neurologic phase either Encephalitic (80%) or Paralytic (20%) Coma/deathThe incubation period is variable and may range from a few weeks to several years; on average it is 1-3 months. In general, bites on the head, face and neck have a shorter incubation period than those elsewhere.
Dog bite
Prodromal Features
The only characteristic feature in the prodromal period is the presence of pain and tingling at the site of the initial wound. Fever, malaise and headache are also present.Encephalitic Rabies (furious)
Manifestations of encephalitic rabies may include fever, confusion, hallucinations, muscle spasms, hyperactivity, and seizures.Autonomic dysfunction is common and may result in hypersalivation and excessive perspiration.
Early brainstem involvement, which results in the classic symptoms of hydrophobia and aerophobia: involuntary, painful contraction of the diaphragm and accessory respiratory, laryngeal, and pharyngeal muscles in response to swallowing liquids (hydrophobia) or a draft of air (aerophobia). Brainstem dysfunction progresses rapidly, and coma followed within days by death is the rule.
Same patient several days later with coma and hypersalivation
Paralytic Rabies (Dumb)
DiagnosisThe diagnosis of rabies is generally made clinically.
Isolation of viruses from saliva or the presence of antibodies in blood or CSF may establish the diagnosis.
Treatment
Once the CNS disease is established, therapy is symptomatic as death is virtually inevitable. The patient should be nursed in a quiet, darkened room. Nutritional, respiratory and cardiovascular support may be necessary.
Drugs such as morphine, diazepam and chlorpromazine should be used liberally in patients who are excitable
Prevention
Post-exposure prophylaxisLocal wound care: The wounds should be thoroughly cleaned, preferably with a quaternary ammonium detergent or soap Tetanus prophylaxis given, and antibiotic treatment initiated whenever indicated, Damaged tissues should be excised and the wound left unsutured. Local wound care is essential and may decrease the risk of rabies virus infection by as much as 90%.
For maximum protection, hyperimmune serum and vaccine are required.
Rabies can usually be prevented if treatment is started within a day or two of biting. Delayed treatment may still be of value. A) Hyperimmune serum: human rabies immune globulin is given in a dose of 20 U/kg body weight. Half is infiltrated around the bite and half is given intramuscularly at a different site from the vaccine.Pre-exposure prophylaxis.
This is given to individuals with a high risk of contracting rabies, such as laboratory workers, animal handlers and veterinarians. Two doses of human diploid cell vaccine (HDCV) given 4 weeks apart provides effective immunity. A reinforcing dose is given after 12 months and then every 1-3 years.B) Vaccine: human diploid cell strain vaccine; 1.0 ml is given intramuscularly on days 0, 3, 7, 14, 30 and 90, This vaccine is safe and free of complications.